1. Field of the Invention
The present invention relates to a wafer polish monitoring method and device, and more particularly, to a wafer polish monitoring method and device that can detect, with high precision, the end point of the polishing of the conductive film formed on a wafer in a chemical mechanical polishing (CMP) process, or the like.
2. Description of the Related Art
An oxide film, for example, is formed on the surface of a semiconductor wafer, and a groove pattern equivalent to a wiring pattern is formed by processing the oxide film by lithography or an etching technique. A conductive film made of Cu or the like is formed thereon to fill the groove pattern. The unnecessary portion of the conductive film is then removed by CMP, so as to form the wiring pattern. This process is a well known process. In the formation of the wiring pattern or the like, it is critical to detect the end point of the polishing with precision and stop the polishing when an appropriate thickness of the unnecessary portion of the conductive film is removed.
As a conventional technique related to the above process, there have been known the following wafer polishing method and device lithography. In a polishing device according to this conventional technique, a platen having a polishing pad attached thereto is rotated, and slurry is supplied onto the polishing pad. While the slurry being supplied, a wafer held by a wafer supporting plate is rotated by the wafer supporting plate, and is pressed against the polishing pad. In this manner, the wafer is polished in this polishing device. More specifically, a groove extending from a point near the center point to a point near the outer periphery is formed in the upper face of the platen, and a through hole widening conically downwards, is formed substantially at the center in the longitudinal direction of the groove. A transparent window member for preventing slurry leakage is embedded in the groove side of the through hole.
A probe is provided on the lower face side of the platen. Light is emitted onto the polished face of the wafer facing the rotating path of the transparent window member, and the probe receives the light reflected by the polished face of the wafer. One end of the probe is connected to an optical cable, and the other end is divided into two ends that are connected to a spectral reflectometer device and a measurement light source. Light is emitted from the measurement light source onto the polished face of the wafer, and the reflected light is introduced into the spectral reflectometer device. The spectral reflection factor with a target film thickness is calculated in advance, and the time when the remaining layer has a desired film thickness is detected when the measured spectral reflection factor becomes equal to the calculated value (see Japanese Patent Application Laid-open (JP-A) No. 7-52032, for example).
There are other known conventional techniques such as the following techniques (a) through (c). (a) Ultrasonic waves of a predetermined oscillating frequency are emitted in a pulse-like fashion in predetermined cycles, and the change in film thickness is measured based on the waves reflected by the surface of the wafer and the interference waves with the waves reflected by the bottom face of the wafer. In this manner, the end point of the polishing process is detected (see JP-A-8-210833, for example).
(b) Electromagnetic waves are supplied to the polishing agent slurry waste, and the resonant frequency and the resonant voltage generated by the waves are measured. Based on the measurement results, the end point of the chemical mechanical polishing process is detected (see JP-A-2002-317826, for example).
(c) The pressure applied to each substrate region is adjusted based on the measurement information about the film thickness of the substrate measured by a film thickness measurement device. The film thickness measurement device is a sensor that utilizes overcurrent, optics, temperature, torque current, microwaves, or the like. However, a sensor utilizing microwaves serves as a film thickness measurement device that measures the film thickness of a Cu film or a barrier film as a conductive film formed on a substrate such as a semiconductor wafer, or the film thickness of an oxide film or the like as an insulating film, using a reflection signal of microwaves alone or a combination of suitable signals (see JP-A-2005-11977, for example).
In accordance with the conventional technique disclosed in JP-A-7-52032, the light reflected by the polished face of the wafer pressed against the polishing pad is introduced into a spectral reflectometer device, and the end point of the polishing is detected based on the spectral reflection factor. However, this method has the problem of reflected light scattering due to the slurry. As a result, the signal-to-noise ratio is poor, and it is difficult to detect the end point of each polishing process with precision.
In accordance with the conventional technique disclosed in JP-A-8-210833, a high-frequency oscillator is provided, however, this high-frequency oscillator supplies a high-frequency signal to an ultrasonic vibrator. Therefore, this high-frequency oscillator is not close to or is not related to the technique in accordance with the present invention for detecting the states before and after the removal of a conductive film formed on a wafer, utilizing the characteristics of transmission and reflection of high-frequency electromagnetic waves with respect to the wafer having the conductive film.
In accordance with the conventional technique disclosed in JP-A-2002-317826, electromagnetic radiation is disclosed. However, this disclosure is not close to or is not related to the technique in accordance with the present invention, as in the case described above.
In accordance with the conventional technique disclosed in JP-A-2005-11977, the film thickness of a conductive film on a substrate and the film thickness of an insulating film are measured with the use of microwaves or the like. However, the present invention differs from the conventional technique disclosed in JP-A-2005-11977 in the following aspects. By the conventional technique disclosed in JP-A-2005-11977, a film thickness with respect to a conductive film is not measured or cannot be measured with precision. Rather, the obvious difference between the waveform observed when a conductive film exists and the waveform observed when the conductive film is removed is utilized. Accordingly, if the end point is set at the time when the conductive film is removed, the end point is detected. Although the use of microwaves is disclosed, the JP-A-2005-11977 does not mention a specific frequency of the microwaves. Therefore, it is not clear whether the characteristics of microwaves are utilized, and there is not a specific disclosure about which features are to be utilized as opposed to electromagnetic waves including general light, and what kind of structure is to be used for the measurement. Furthermore, there is not a clear definition of “reflection of microwaves”. For example, there is not a disclosure about the fact that the transmission and reflection states are changed as the characteristic impedance is varied by the existence of a conductive film on the wafer in the formation of a high-frequency transmission line for transmitting microwaves. As an example method, a microstrip line serving as a high-frequency transmission line extending along a wafer is provided, as disclosed in the present invention. In the description, it is defined that electromagnetic waves that pass through the microstrip line are set as transmitted electromagnetic waves, and electromagnetic waves that are reflected due to impedance mismatching without entering the high-frequency transmission line are set as reflected electromagnetic waves. Also, there is another method that a transmission antenna and a reception antenna are prepared, so as to perform evaluations based on the signal intensity between the two antennas. However, any of those methods is not disclosed in JP-A-2005-11977. Therefore, it is reasonable to say that the microwaves disclosed in JP-A-2005-11977 may be regarded as electromagnetic waves including general light. Also, in accordance with the present invention, a film thickness exceeding a skin depth is not to be measured, and the states before and after the removal of the conductive film on a wafer are detected with high precision, based on the large difference between the transmission and reflection characteristics of electromagnetic waves between a conductive film and a nonconductive film. Accordingly, the present invention greatly differs from the conventional technique, in terms of the structure, actions, and effects.